The present invention is related to a high contrast ratio reflective STN LCD structure in which the liquid crystal molecules have smaller torsion angle and the retardation value of the liquid crystal molecules is controlled within 580 nm to 650 nm.
FIG. 4 shows a conventional reflective liquid crystal display (LCD). One single optical deflector 71 is laid over an upper glass panel 7. A reflector 82 is laid over a lower glass panel 8 for reflecting light and eliminating parallex so as to promote displaying quality of the LCD. However, at least two phase compensating films 72 are disposed under the single optical deflector 71. The two layers of phase compensating films 72 have different retardation values, in which the lower phase compensating film 72 has a retardation value within 100 nm to 180 nm, while the upper phase compensating film 72 has a retardation value within 200 nm to 360 nm. In phase coupling, such structure will encounter complicated problem of phase compensation and it is relatively difficult to manufacture such product. As a result, the ratio of defective product is higher.
Moreover, the liquid crystal molecules 81 of the liquid crystal layer 8 have high torsion angle within 220xc2x0 to 240xc2x0. This leads to higher spectrum of the liquid crystal layer 8. The phase compensating films 72 are unable to totally phase-compensate the entire range of light (different colors with different wavelengths). This results in leakage of light in dark-state and lowers the contrast ratio effect of the LCD.
It is therefore a primary object of the present invention to provide a high contrast ratio reflective STN LCD structure which includes only one optical deflector. The liquid crystal molecules of the LCD have smaller torsion angle, whereby the penetration ratios of lights with different wavelengths can be lowered to be proximate to 0%. Accordingly, the leakage of light in dark-state is reduced and the contrast ratio is enhanced. Therefore, the spectrum of the liquid crystal layer can be effectively controlled and it is unnecessary to use two or more phase compensating films. The manufacturing procedure is thus simplified and the ratio of good product is increased.